U.S. patent application number 10/428666 was filed with the patent office on 2003-11-13 for tubular membrane module.
This patent application is currently assigned to DaimlerChrysler AG. Invention is credited to Poschmann, Thomas.
Application Number | 20030209481 10/428666 |
Document ID | / |
Family ID | 29285201 |
Filed Date | 2003-11-13 |
United States Patent
Application |
20030209481 |
Kind Code |
A1 |
Poschmann, Thomas |
November 13, 2003 |
Tubular membrane module
Abstract
A tubular membrane module includes a a tubular jacket delimiting
a flow path for a fluid containing a plurality of components, a
plurality of tubular membrane bodies bundled together in a bundle
and disposed in the tubular jacket, and at least one interspace
element disposed between at least two adjacent membrane bodies of
the plurality of membrane bodies. Each of the tubular membrane
bodies has a surface and is permeable for a first component of the
plurality of components. The interspace elements reduces a
diffusion path of the first component to the surface of the
membrane bodies.
Inventors: |
Poschmann, Thomas; (Ulm,
DE) |
Correspondence
Address: |
DAVIDSON, DAVIDSON & KAPPEL, LLC
485 SEVENTH AVENUE, 14TH FLOOR
NEW YORK
NY
10018
US
|
Assignee: |
DaimlerChrysler AG
Stuttgart
DE
|
Family ID: |
29285201 |
Appl. No.: |
10/428666 |
Filed: |
May 2, 2003 |
Current U.S.
Class: |
210/321.8 ;
210/321.89 |
Current CPC
Class: |
B01D 53/22 20130101;
B01D 63/06 20130101; B01D 2321/2016 20130101; B01D 65/08 20130101;
C01B 2203/041 20130101; C01B 3/501 20130101; B01D 2313/22
20130101 |
Class at
Publication: |
210/321.8 ;
210/321.89 |
International
Class: |
B01D 063/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 8, 2002 |
DE |
102 20 505.1 |
Claims
What is claimed is:
1. A tubular membrane module, comprising: a tubular jacket
delimiting a flow path for a fluid containing a plurality of
components; a plurality of tubular membrane bodies bundled together
in a bundle and disposed in the tubular jacket, each of the tubular
membrane bodies having a surface and being permeable for a first
component of the plurality of components; an interspace element
disposed between at least two adjacent membrane bodies of the
plurality of membrane bodies so as to reduce a diffusion path of
the first component to the surface of the membrane bodies.
2. The tubular membrane module as recited in claim 1, wherein the
plurality of tubular membrane bodies define a length, and the
interspace element extends over the length.
3. The tubular membrane module as recited in claim 1, the
interspace element has a shape adapted to a contour of the adjacent
membrane bodies.
4. The tubular membrane module as recited in claim 1, wherein an
outside of the interspace element includes a structure configured
to induce a turbulence in the fluid.
5. The tubular membrane module as recited in claim 1, wherein the
interspace element is a tubular hollow body.
6. The tubular membrane module as recited in claim 1, wherein the
interspace element includes a supplemental membrane body permeable
for a second component of the plurality of components.
7. The tubular membrane module as recited in claim 5, wherein the
interspace element is configured to feed a second fluid into the
tubular jacket through the interspace element.
8. The tubular membrane module as recited in claim 7, wherein the
interspace element includes inlet openings.
9. The tubular membrane module as recited in claim 7, wherein the
interspace element is porous.
10. The tubular membrane module as recited in claim 1, wherein the
interspace element is configured to heat the tubular membrane
module.
11. The tubular membrane module as recited in claim 10, wherein the
interspace element includes a catalytically active component
disposed inside the interspace element.
12. The tubular membrane module as recited in claim 10, wherein the
catalytically active component is in the form of one of a coating
or a packing.
13. The tubular membrane module as recited in claim 1, wherein the
tubular jacket includes a geometry adapted to an outside contour of
the bundle.
14. The tubular membrane module as recited in claim 1, wherein the
tubular jacket includes a structure disposed on an inside of the
tubular jacket configured to induce a turbulence in the fluid.
15. The tubular membrane module as recited in claim 1, wherein the
tubular membrane module forms a part of a gas generating
system.
16. The tubular membrane module as recited in claim 15, wherein the
gas generating system includes a system to generate a
hydrogen-containing gas by reforming hydrocarbons, and wherein the
interspace element is configured to feed a component involved in
the reforming.
17. The tubular membrane module as recited in claim 1, wherein the
tubular membrane module forms a part of a gas generating system for
a fuel cell systems, and wherein at least one of a
hydrogen-containing anode exhaust gas and a hydrogen-containing
raffinate of the gas generating system are introduced with air into
the interspace element so as to heat the tubular membrane module.
Description
[0001] Priority is claimed to German Patent Application No. DE 102
20 505.1, filed May 8, 2002, which is incorporated by reference
herein.
BACKGROUND
[0002] The present invention relates to a tubular membrane module
having a plurality of tubular membrane bodies bundled together in a
common tubular jacket. The tubular jacket delimits a flow path for
a fluid containing multiple components. The membrane bodies are
permeable for at least one component of this fluid to be
separated.
[0003] Such tubular membrane modules are used, for example, in
conjunction with gas generating systems in which hydrocarbons are
reformed to produce a gas containing hydrogen. In this application,
the tubular membrane modules are equipped with highly permeable
membrane bodies and are used to separate hydrogen from the
reformate gases.
[0004] When using tubular membrane modules, module effects may
occur, having an overall negative effect on the permeation
efficiency of the module. The effect of concentration polarization
in particular prevents the maximum achievable theoretical
permeation rate from being in fact achieved.
[0005] The prerequisite for permeation is a concentration gradient
across the membrane, i.e., the gradient of the chemical potential
across the membrane. Permeation performance is greater, the greater
the concentration gradient. In the case of concentration
polarization, the diffusivity of the fluid is not sufficient to
ensure a uniform concentration of the permeating component in the
entire feed space of the membrane. Permeation here leads to a drop
in concentration of the permeating component of the fluid on the
membrane surface, so that concentration C.sub.S of the permeating
component on the membrane surface is lower than concentration
C.sub.F of the bulk flow in the feed space, which is illustrated
schematically in FIG. 1. This concentration gradient results in the
development of a concentration boundary layer in the feed space of
the membrane and has a negative effect on the permeation
performance of the module.
[0006] It has been assumed in the past that effects such as
concentration polarization may be disregarded in gas permeation
because gases have a high diffusion coefficient. However, it has
been found that the high diffusivity of gases in highly permeable
membranes such as those used for separation of hydrogen, for
example, is not sufficient to ensure a sufficiently rapid mass
transport to the membrane.
[0007] The present invention proposes a tubular membrane module
with which very good permeation rates may be achieved because the
structure of the tubular membrane module according to the present
invention counteracts permeation-reducing effects and concentration
polarization in particular.
[0008] This is achieved according to the present invention by
providing at least one interspace element between the membrane
bodies of the bundled arrangement, thereby reducing the diffusion
path to the surface of the membrane bodies for the component of the
fluid to be separated.
[0009] It has been recognized according to the present invention
that the effect of concentration polarization may be effectively
suppressed by reducing the diffusion path of the component to be
separated. Furthermore, it has been recognized according to the
present invention that the surfaces of adjacent membrane bodies
with the known tubular membrane modules are not usually spaced an
equal distance apart at all points, so this results in diffusion
paths of different lengths for different areas of the bundle
arrangement. Including interspace elements according to the present
invention in the bundle arrangement of the membrane bodies thus
permits not only a reduction in the diffusion path of the component
to be separated, but also an equalization of the length of the
diffusion path, depending on the arrangement of the interspace
elements and in particular also depending on the adaptation of the
shape of the interspace elements to the geometry of the membrane
bodies.
[0010] As already indicated, there are various possibilities for
designing the interspace elements within the scope of the present
invention. Advantageously, they extend essentially over the entire
length of the membrane bodies of the tubular membrane module. With
regard to an equally long or short diffusion path, preferably in
all regions of the tubular membrane module, it has proven
advantageous for the shape of the interspace elements to be adapted
to the contour of the adjacent membrane bodies. In an advantageous
variant of the tubular membrane module according to the present
invention, the outsides of the interspace elements are provided
with a structure to induce turbulence in the fluid flow. Such
turbulence promotes transport of the component to be separated
toward a membrane body and counteracts the development of a
concentration boundary layer.
[0011] Since the interspace elements function primarily to reduce
the diffusion path of the component of the fluid to be separated,
they may in principle be designed as either solid or hollow
elements made of any desired material, preferably inert. However,
from the standpoint of a lightweight design of the tubular membrane
module according to the present invention and also from the
standpoint of any additional functions of the interspace elements,
it has proven advantageous for the interspace elements to be
designed as tubular hollow bodies.
[0012] In an advantageous variant of the tubular membrane module
according to the present invention, the interspace elements are
also implemented in the form of membrane bodies which are permeable
for either the component of the fluid to be separated or another
component of the fluid. In this case, the bundle arrangement
includes membrane bodies which differ at least in cross-sectional
shape and/or cross-sectional size.
[0013] In another variant of the tubular membrane module according
to the present invention, the wall of the tubular interspace
elements has inlet openings or is porous so that another fluid may
be fed into the tubular jacket through these interspace elements.
This has proven to be advantageous in reforming hydrocarbons in
particular, when the tubular membrane module is designed as a
membrane reactor. To do so, a catalyst packing is provided in the
feed space of the membrane bodies. Then individual components
involved in reforming, e.g., hydrocarbons, water and air, may be
added through the interspace elements.
[0014] However, these interspace elements may also be used to heat
the tubular membrane module according to the present invention. To
do so, the inside of the tubular interspace elements may be
provided with a catalytically active coating or a catalytically
active packing may be provided in the interior of the tubular
interspace elements to permit internal heating of the tubular
membrane module. If the tubular membrane module according to the
present invention is used as part of a gas generating system for
fuel cell systems, then the hydrogen-containing anode exhaust gas
of the fuel cell or the hydrogen-containing raffinate of the gas
generating system may be introduced with the addition of air into
the interior of the interspace elements, where a reaction
associated with the evolution of heat then takes place.
[0015] The development of concentration boundary layers on the
outside of the membrane body bundle may be effectively counteracted
by adapting the geometry of the tubular jacket to the outside
contour of the membrane body bundle. In this connection, it has
also proven advantageous if the inside of the tubular jacket is
provided with a structure to induce turbulence in the fluid
flow.
[0016] As already explained in detail above, there are various
possibilities of embodying and improving upon the teaching of the
present invention in an advantageous manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Reference is made to the claims and to the following
description of an exemplary embodiment of the present invention
with reference to the drawings, in which:
[0018] FIG. 1 shows a schematic diagram of the phenomenon of
concentration polarization, which was explained above as part of
the introduction to the description;
[0019] FIG. 2 shows a section through a tubular membrane module
known from practice (related art), and
[0020] FIG. 3 shows a section through a tubular membrane module
according to the present invention.
DETAILED DESCRIPTION
[0021] Tubular membrane module 10 shown in FIG. 2 is used in
general to separate one component from a fluid containing multiple
components. In practice, such tubular membrane modules are used to
separate hydrogen from hydrogen-rich reformate gases for motor
vehicles operated with fuel cells, for example. The functioning of
tubular membrane module 10 is explained below on the basis of this
example of an application.
[0022] Tubular membrane module 10 includes seven tubular membrane
bodies 11, only five of which are shown here. All membrane bodies
11 have the same circular cross section and are bundled together in
a common tubular jacket 12, which also has a circular cross
section. To separate hydrogen, the hydrogen-rich reformate gas is
fed into tubular jacket 12, so that the reformate gas flows through
tubular jacket 12. In doing so, hydrogen accumulates in the
interior of membrane bodies 11 because the walls of membrane bodies
11 are permeable for hydrogen due to their material and properties,
and there is a hydrogen concentration gradient between the outside
of membrane bodies 11 and the inside of membrane bodies 11. On the
whole, hydrogen permeates through the walls of membrane bodies 11
more rapidly here than do the other components of the reformate
gas.
[0023] FIG. 2 shows the arrangement of membrane bodies 11,
including packing-induced regions 13 where the diffusion path to
the wall of the next membrane body 11 is greater than in other
regions of the bundled arrangement. These regions 13 are especially
susceptible to developing concentration polarization.
[0024] Tubular membrane module 1 according to the present
invention, as illustrated in FIG. 3, also includes seven tubular
membrane bodies 2, only five of which are shown here. Here again,
all membrane bodies 2 have the same circular cross section and are
bundled together in a common tubular jacket 3a and/or 3b. The
arrangement of membrane bodies 2 in this exemplary embodiment of
the present invention thus corresponds to the bundled arrangement
illustrated in FIG. 2.
[0025] However, in the case of tubular membrane module 1 according
to the present invention, interspace elements 4 are provided
between membrane bodies 2 in regions 13, thereby reducing the feed
space and thus the diffusion path to the surface of the next
membrane body 2. This measure counteracts the development of
concentration polarization in regions 13.
[0026] Tubular membrane module 1 could reasonably include five
interspace elements 4, although only two are shown in FIG. 3.
[0027] Interspace elements 4 are designed here in the form of tubes
having a circular cross section that is smaller than the cross
section of membrane bodies 2. The interspace elements could of
course also be designed as solid elements and/or they could have
some other shape, e.g., adapted to the contour of the adjacent
membrane bodies.
[0028] As already explained in detail in the introduction to the
description, interspace elements 4 may also have another function
in addition to that of reducing the feed space. For example, the
interspace elements may also be implemented in the form of membrane
bodies, or they may be used for feeding another fluid into the
tubular jacket. However, the interspace elements may also be used,
e.g., to heat the tubular membrane module.
[0029] FIG. 3 shows two possibilities for implementing a tubular
jacket 3a and/or 3b of tubular membrane module 1 according to the
present invention. Tubular jacket 3a has a circular cross section
and corresponds essentially to tubular jacket 12 shown in FIG. 2.
In contrast with that, the geometry of tubular jacket 3b is adapted
to the outside contour of the membrane body bundle.
[0030] In conclusion, it should be pointed out that the cross
section of the membrane bodies of a tubular membrane module
according to the present invention need not be circular but may
also have any other shape. Furthermore, not all membrane bodies of
a tubular membrane module according to the present invention must
have the same cross-sectional shape and size. The number of
membrane bodies and interspace elements combined in a tubular
membrane module according to the present invention may be varied at
will.
* * * * *